1888-89.] Mr A. Johnstone on Action of Sea- Water. 
173 
'point of saturation. Fresh spring, river, or lake waters containing 
alkaline carbonates in solution are also, as my experiments prove, 
totally unable to decompose pure natural silicate of magnesia. 
Of course, it must be remembered that the amount of alkaline 
carbonate in natural waters is very small. In the Loire, near 
Orleans, Deville was able to find only 1*46 parts of carbonate of 
soda in 100,000 parts of water ; while in the Garonne, near Toulouse, 
the same chemist could only detect 065 part of alkaline carbonate 
in 100,000 of water. 
Sea-water, however, and also the waters of salt lakes and brinel 
springs, i.e ., all waters which contain a considerable amount of 
sodium chloride in solution, act chemically on pure mineral mag- 
nesium silicates. This fact I have clearly ascertained by the follow- 
ing experiment. 
I allowed a litre of a nearly saturated pure aqueous solution of 
pure sodium chloride to act for two months on a thin fragment 
(presenting a fairly large surface) of pure and thoroughly clean 
white steatite (4Mg"Si0 3 .Si0 2 ). On the expiry of that period I 
removed the mineral from its bath, filtered the liquid in which it 
had lain very carefully, and proceeded to test it chemically, with 
the object of discovering whether magnesia had been dissolved out 
of the steatite by the action of the salt solution or not. 
I acidulated a portion of the clear filtered liquid with nitric acid, 
and then added excess of ammonium hydrate, and after mixing the 
whole properly, filtered at once. Into the filtrate I now poured 
some ammonium phosphate solution, agitated the mixture violently 
for several minutes, and then put it aside to allow it to settle for 
about a quarter of an hour. By the end of that time a little, but 
a very distinct, white crystalline precipitate, indicative of the pre- 
sence of magnesia, had fallen to the bottom of the vessel. This 
white crystalline powder was afterwards examined under the 
microscope, and was found to consist mainly of translucent prisms 
belonging to the trimetric system. Thus the microscope confirmed 
the chemical test. The remainder of the clear solution in which 
the steatite had lain was evaporated to dryness, and the sodium 
chloride and magnesium salt of the residue were completely dis- 
solved out by means of dilute hydrochloric acid. After this had 
been accomplished there still remained a trace of residue which 
